Green’s Dictionary of Slang

sweetener n.2

1. a gratuity; a bribe.

[UK]Egan Finish to the Adventures of Tom and Jerry (1889) 189: You must tip. It is the sort of sweetener we folks expect, to make everything right!
[Aus][A. Harris] (con. 1820s) Settlers & Convicts 89: The handsome ‘sweeteners’ (bribes) which old D—’s profits enabled him to give to the constables .
[UK]Western Dly Press 17 Apr. 3/5: ‘Sweeteners’ to government Officials [...] The first thing said to him by the contractor was ‘I suppose, sir, you expect the usual 2½ per cent commission?’ This meant a preliminary present, or ‘sweetener’ of £5,000.
[UK]Manchester Eve. News 10 Jan. 2/3: Diplomacy, which in this instance assumed the shape of a money bribe and an even more effectual ‘sweetener’ in the shape of duty free rum and gin.
[US](con. 1910–20s) D. Mackenzie Hell’s Kitchen 120: Sweetener ... a gratuity; bribe; also refers to coaxing.
[UK]Dundee Courier 16 Aug. 2/2: Now it seems that the Argentinian cattle-breeders got only two-thirds of their £10,000,000 sweetener from their Government.
[UK]B. Hill Boss of Britain’s Underworld 3: A thief had to pay many sorts of people [...] bribes and sweeteners.
[UK]J. Morton Lowspeak.
[UK]J.J. Connolly Viva La Madness 367: I’d made a point of transferring the sweetener [...] to an account I held in the Jamaican branch of a Canadian bank.

2. an encouragement.

[UK]Leaves from Diary of Celebrated Burglar 147/2: This was indeed anything but a ‘sweetener.’ The bare idea of such a loss prevented us sleeping at night.

3. (US) a drink.

[US]Spirit of the Times (N.Y.) 18 Mar. in A.P. Hudson Humor of the Old Deep South (1936) 43: Let’s take a sweetener and go to bed.

4. a hard blow.

[Aus]Bell’s Life in Sydney 18 Mar. 1/4: Terry [...] popped a sweetener on the ivories.
[US]H.L. Williams Night in the New Hotel in Darkey Drama 4 43: I’ll gib you one ob my sweeteners if you don’t chain up! (flourishes umbrella).

5. a scolding, a ‘talking-to’.

[Aus]Bell’s Life in Sydney 28 Nov. 3/3: After a ‘sweetener’ from the Captain, Kitty was discharged and her man of business bound over the keep the peace.
[US]A.F. Hill Our Boys 145: The colonel [...] with an oath commonly called a ‘sweetener,’ roared out peremptorily: ‘Who the h-ll fired that gun?’.

6. (UK Und.) in pl., the lips.

[UK]Farmer & Henley Sl. and Its Analogues.

7. the penis.

[UK]Lustful Memoirs of a Young and Passionated Girl 24: When he saw by her countenance that she was beginning to feel some pleasure he began slowly to move his sweetener out and in.